JPH0773714B2 - Wastewater nitrification method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for nitrifying wastewater, and more particularly to a method for biologically nitrifying an organic wastewater containing ammonia.

[Prior Art] Conventionally, ammonium ions in the waste water in the biological denitrification process ammonia human waste such as non-organic waste water (NH ₄ ⁺⁾ are all nitrite ions (NO ₂ ^-), more nitrate ( NO ₃ ^- after being nitrification in), which is denitrification in N _2.

On the other hand, as a chemical denitrification process, ammonium ions by the following reaction (NH ₄ ⁺⁾ nitrite ions denitrification reaction of _{→ N 2 + 2H 2 O ...} (I) - (NO 2 -) NH 4 + + NO 2 from The method is known. For example, in Rinzo Chitani, "Inorganic Chemistry," Chapter 13, page 600, the following reaction formula NH ₄ NO ₂ → N ₂ + 2H ₂ O… (II) is given as an example of a method for producing pure chemical nitrogen. The concentrated aqueous solution is heated to 70 ° C and NH ₄ NO ₂
It is described to decompose. It has also been reported that the above reaction proceeds even at room temperature by using a ferric salt or the like as a catalyst.

By adopting the chemical denitrification process by the reaction shown in the above formula (I), it is possible to reduce the required oxygen amount and reduce the treatment cost. However, such a chemical denitrification process is adopted. In order to do so, it is necessary to stop the nitrification of NH ₄ ⁺ at 50% and use nitrification treated water with NH ₄ ⁺ / NO ₂ ⁻ = 1.

In addition, as a method of removing nitrogen in one step, a method of oxidizing ammonia to nitrous acid by using immobilized nitrite bacteria and at the same time catalytically oxidizing the generated nitrous acid has been proposed (JP-A-62-197196).

[Problems to be Solved by the Invention] According to the method described in JP-A-62-197196, it is difficult to carry out catalytic oxidation at room temperature. On the other hand, when catalytically oxidized by heating, immobilized bacteria die due to heat. There is a problem that it ends up.

On the other hand, as described above, in order to adopt a chemical denitrification process, stop the nitrification in ^{_{50%, NH 4 + / NO}} 2 - = 1 for it is necessary to obtain the nitrification treated water, in the conventional nitrification No effective method has been proposed to keep the rate at just 50% and make the treated water NH ₄ ⁺ / NO ₂ ⁻ = 1.

It is known that nitrification can be suppressed by lowering the pH of the nitrification tank, but it is not possible to stop the nitrification rate at a desired value by merely controlling the pH. That is, in the wastewater, the pH is usually
Since it contains a compound having a buffering power, such as bicarbonate, carbonate, and phosphate, it is very difficult to control the nitrification rate by pH control.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a nitrification method for wastewater, which can control the nitrification rate to a desired value.

[Means for Solving the Problems] A method for nitrifying wastewater of the present invention is a method for biologically nitrifying an organic wastewater containing ammonia, in which the ammonia concentration and alkalinity of the wastewater are measured, and the equivalent ratio of both is measured. It is characterized in that an acid or an alkali is added to achieve a predetermined value and nitrification is performed by nitrifying bacteria to control the nitrification rate.

In the present invention, the type of acid or alkali to be added is not particularly limited, and as the acid, hydrochloric acid, sulfuric acid, etc.,
Further, as the alkali, NaOH, KOH or the like can be used.

The method of the present invention measures the ammonia concentration and alkalinity of wastewater, and controls the nitrification rate by adding a predetermined amount of acid or alkali to the wastewater or nitrification tank so that the equivalent ratio becomes a predetermined value. .

For example, if the equivalent ratio of ammonia concentration and alkalinity of wastewater is 1, the nitrification rate is 50%, and if the equivalent ratio of ammonia concentration and alkalinity is less than 1, the nitrification rate is over 50%. When the equivalent ratio of ammonia concentration and alkalinity exceeds 1, the nitrification rate can be less than 50%. The ammonia concentration can be measured by a conventional method such as the indophenol blue method or titration method, and the alkalinity can be easily measured by titration using a mixed indicator of methyl red and bromcresol gulin (discoloration point pH 4.8). You can

[Operation] The method of the present invention will be described in detail by explaining the operation and effect of the present invention.

As described above, there are substances having various pH buffering properties, that is, buffers such as bicarbonates, carbonates and phosphates in the waste water. Then, as nitrification progresses and NO ₂ ⁻ ions are generated,
The buffer is consumed. When all the buffer is consumed, the pH drops sharply and nitrification stops. Therefore, in the wastewater
Measure NH ₄ ⁺ concentration and buffer concentration, that is, alkalinity,
By adding an acid or an alkali to adjust this equivalence ratio, the buffer can be adjusted and the nitrification rate can be set to a desired value. That is, when the ammonia concentration and alkalinity and the like equivalent in wastewater is a buffer at the stage where NH ₄ ⁺ half in the wastewater is generated NH ₄ NO ₂ is nitrification _{(NH 4 / NO 2 = 1} ) Since it does not remain, the pH drops and nitrification stops, resulting in a nitrification rate of 50%. Further, when the ammonia concentration is higher than the alkalinity, NH ₄ ⁺ remains when the buffer is nitrified and nitrification is stopped when the nitrification rate is lower, and the nitrification rate is less than 50%. On the other hand, when the ammonia concentration is lower than the alkalinity, even when the nitrification has progressed to half,
Since the buffer remains, the pH does not decrease, nitrification further progresses, and the nitrification rate exceeds 50%.

In the following, according to the method of the present invention, the nitrification rate was set to 50%, and NH
_The effect of obtaining treated water with ₄ / NO ₂ = 1 will be described.

The biological nitrification reaction is represented by the following basic formula.

NH ₄ ⁺ ＋ 3 / 2O ₂ → NO ₂ ⁻ ＋ H ₂ O ＋ 2H ⁺ (III) Conventionally, in order to prevent the decrease of pH due to H ⁺ produced, pH control is usually performed to perform 100% nitrification.

On the other hand, the form of N in wastewater is mostly organic-N, NH ₄ -N,
The source of its generation is due to the decomposition of amino groups of proteins. When BOD coexisting in the waste water is subjected to oxidation of the microorganisms, there is the generation of CO _2, which the NH ₄ ⁺ are bonded, form of NH ₄ after it has received the biological treatment becomes NH ₄ HCO _3. The reaction formula for the nitrification reaction of NH ₄ HCO ₃ without adjusting the pH is as follows.

NH ₄ HCO ₃ ＋ 3 / 4O ₂ → 1/2 NH ₄ NO ₂ ＋ 3 / 2H ₂ O + CO ₂ …… (IV) When NH ₄ NO ₂ is produced, all NH ₄ HCO _{3 in the} raw water is consumed, and other than this If the buffer is not in the liquid, the pH will drop and nitrification will stop. That is, the reaction spontaneously stops when NH ₄ / NO ₂ = 1.

However, all the actual wastewater was used as a buffer for NH ₄ H.
CO ₃ not necessarily be composed only of, for example, some that only NH ₄ ⁺ flows from such industrial waste water, HCO ₃ ^-
Other buffers (eg phosphate buffer etc.) may be present. In such a case, when the reaction is carried out without pH adjustment, the end point is NH ₄ /
NO ₂ > 1, and in the latter case NH ₄ / NO ₂ <1, NH ₄ /
Water with NO ₂ = 1 cannot be obtained.

Therefore, in order to set NH ₄ / NO ₂ = 1 for all wastewater, it is necessary to measure the NH ₄ ⁺ concentration and the buffer amount of the liquid, that is, the alkalinity, and adjust the equivalent ratio in advance. . That is, in the former example, by adding a predetermined amount of alkali,
In the latter case, acid is added to offset the buffer.

Thus, according to the present invention, the ammonia concentration and alkalinity of the wastewater are measured, and acid or alkali is added so that the equivalent ratio of the two becomes 1, and nitrification by nitrifying bacteria is performed to obtain a nitrification rate of 50%. As a result, it is possible to obtain treated water with NH ₄ / NO ₂ = 1. In this case, nitrite type nitrification and NH
By performing chemical decomposition of ₄ NO ₂ in stages, it is possible to carry out efficient nitrification and denitrification.

It should be noted that the method of the present invention, as described above, not only in the case of controlling the nitrification rate of 50%, a nitrification rate as other values, NH ₄ / NO ₂
Needless to say, the present invention can be applied to the case of obtaining treated water other than 1.

[Examples] The present invention will be described more specifically with reference to Examples.

Example 1 Human waste anaerobic digestion treated water (Run1), petroleum refinery wastewater (Run
2) and wastewater with high alkalinity (Run3) as raw water,
The treatment was performed with nitrifying bacteria (filling rate: 30% by weight) immobilized on polymer gels, with retention times of 2 days, 18 hours and 5 hours, respectively.

The method for immobilizing nitrifying bacteria is as follows.

First, 10 g (wet weight) of accumulated nitrifying bacteria was added to a solution A having the following composition.
Was thoroughly mixed with 100 ml of the above, and this was added dropwise to 1 of solution B (ice-cooled) having the following composition. After leaving it in this state for 1 hour, it was dipped in a solution C having the following composition for 30 minutes to dissolve alginic acid, then thoroughly washed with 1/50 M Tris buffer (pH 8), and stored in a refrigerator.

Solution A Polyacrylic hydrazide (average molecular weight 183): 3% by weight Sodium alginate: 0.5% by weight 1 / 50M Tris buffer (pH 8) Solution B CaCl ₂ · 2H ₂ O: 2% by weight Glyoxal: 0.1% by weight 1 / 50M Tris buffer (PH8) Solution C K ₂ HPO ₄ : 1.46% by weight KH ₂ PO ₄ : 0.226% by weight 1 / 50M Tris buffer (pH 8) DO ₂ was used at the beginning of the operation in order to operate NO ₂ type nitrification.
(Dissolved oxygen) was set to <0.2, and normal DO operation was switched to when NO ₂ ⁻ accumulation was observed. Table 1 shows the NH ₄ —N concentration and alkalinity of each wastewater. Table 2 shows the average water quality of treated water after operating for about 2 months without pH adjustment.

As is clear from Tables 1 and 2, due to the difference in the original alkalinity of the wastewater, NH ₄ ⁺ -
N / NO ₂ ^- -N varied greatly 0.1-15.

Therefore, 70 mg of NaOH was added to the raw water of Run 2 which lacked alkalinity.
Equivalent / Also, 1 H ₂ SO ₄ for Run 3 with excess alkalinity
5mg where eq / was continuously added in a few days, NH ₄ ⁺ -N / NO ₂ of treated water ^- was the -N ≒ 1.

In addition, when the treated water of Run 1 was heated to 120 ° C. for 1 hour,
NH ₄ ⁺ -N in the treated water 15mg equivalent /, NO ₂ ^- -N is 8mg eq / next, the chemical denitrification by formula (I) occur, good treated water was obtained.

[Effects of the Invention] As described in detail above, according to the method for nitrifying wastewater of the present invention,
The nitrification rate can be easily and reliably controlled to a desired value.

Therefore, by employing the method of the present invention, to suppress the nitrification rate of 50% nitrification as nitrite-type ^{_{nitrification, NH 4 + -N / NO 2}} -
It is possible to obtain treated water of −N≈1, and it is possible to nitrify and denitrify the wastewater easily and at low cost by applying the chemical denitrification process.

Claims (1)

[Claims] 1. In a method for biologically nitrifying an organic wastewater containing ammonia, the ammonia concentration and alkalinity of the wastewater are measured, and an acid or alkali is added so that the equivalent ratio of the two becomes a predetermined value. Nitrification by nitrifying bacteria to control the nitrification rate.